The present invention relates to the field of compositions that can be used in the manufacture of hot-melt adhesives.
In general, a hot-melt adhesive is manufactured from a mixture comprising three essential components:
a petroleum resin having a tackifying effect, PA1 a thermoplastic resin capable of providing the cohesion of the mixture, and PA1 a paraffin or a microcrystalline polymeric wax capable of adapting the viscosity of the mixture to the processing and use conditions of the adhesive. PA1 (a) 100 parts by weight of a petroleum wax reinforced by an ethylene/C.sub.3 -C.sub.18 .alpha.-olefine copolymer, and PA1 (b) an adhesion-promoting system consisting of a mixture of 25 to 50 parts by weight of a tackifying resin and 10 to 30 parts by weight of a polar polymeric additive. This additive is selected from: PA1 (a) from 20 to 45 parts of at least one tackifying resin, PA1 (b) from 0 to 45 parts of at least one compound selected from paraffin, microcrystalline polymeric wax, and esters of a hydrogenated rosinic acid and of a lower alcohol, and PA1 (c) from 20 to 70 parts comprising a terpolymer of ethylene having a melt index between 5 and 500 dg/minute and comprising:
To choose the thermoplastic resin forming part of this mixture, good properties are sought both in respect to heat stability and in respect to adhesiveness. The thermoplastic resins commonly used in compositions for the manufacture of hot-melt adhesives have been on the one hand, copolymers of ethylene and vinyl esters, in particular vinyl acetate, and, on the other hand, copolymers of ethylene and alkyl acrylates, in particular ethyl acrylate and butyl acrylate.
For example, U.S. Pat. No. 3,869,416 describes an adhesive composition comprising:
copolymers of ethylene and vinyl esters, PA2 copolymers comprising at least 85 mol % of ethylene and at least 7 mol % of alkyl (meth)acrylates, and PA2 copolymers comprising at least 85 mol % of ethylene and from 0.15 to 5 mol % of carboxylic acids, carboxylic acid partial esters, or carboxylic anhydrides (methacrylic acid and maleic anhydride are preferred). PA2 from 1 to 10 mol% of units derived from an ester selected from alkyl acrylates and methacrylates, said alkyl group having from 1 to 6 carbon atoms, and from 0.3 to 3 mol% of units derived from maleic anhydride.
The users of hot-melt adhesives are constantly seeking to improve their properties, in particular their adhesiveness on a given substrate and their ability to adhere to very diverse types of substrate. From this viewpoint, the compositions previously used are not satisfactory, irrespective of the type of substrate in question. For example, a hot-melt adhesive manufactured from a composition comprising a copolymer of ethylene and vinyl acetate has good adhesiveness on leather and on a panel made of agglomerated particles, but moderate adhesiveness on rubber, poor adhesiveness on polyvinyl chloride, aluminum, and steel, and very poor adhesiveness on glass.